How much light is generated by cherenkov radiation from a single high energy neutrino? I'm guessing that if these detectors (PMTs?) are frozen into cryogenic ice they probably have insanely low dark counts so maybe not much. Would it be enough to see by eye if you happened to be looking in the right place at the right time? Just a flash of light?

So I'm curious, energy can neither be created nor destroyed, but apparently it's OK to move it into a place where it rarely interacts with normal matter. Does this have any implications for our beloved laws of thermodynamics?

So I'm curious, energy can neither be created nor destroyed, but apparently it's OK to move it into a place where it rarely interacts with normal matter. Does this have any implications for our beloved laws of thermodynamics?

Nope. Physics remains unviolated. You may wish to look into the idea of the heat death of the universe:

So I'm curious, energy can neither be created nor destroyed, but apparently it's OK to move it into a place where it rarely interacts with normal matter. Does this have any implications for our beloved laws of thermodynamics?

Don't see how, unless there is a way to force it to interact.

Thermodynamic, if i understand it right, is about two pools of energy. One high, one low. the difference between the two are then used to produce changes as a by product of leveling out the difference. Said changes will never be effective enough to counteract the leveling, ruling out perpetual motion.

As heat is considered the lowest state in all this, you get the expression "heat death of the universe".

All in all i suspect neutrinos, no matter how energetic, can be considered to be very close to heat in all this. So unless we have exhausted all other options, using high energy neutrinos as the high pool is likely an act of futility.

It should be noted more explicitly that these are potentially signatures of 'extra-galactic' neutrinos, compared to normal galactic neutrinos which have lower energies (though higher than solar neutrinos).

Can these detectors determine the direction the neutrinos came from, or only their magnitude? What would it take to be able to determine the source?

Since they have a grid, they should be able to determine direction. You'd need counts along the particles path.

Are the resultant particles' paths dependent on the original neutrino's path?

These particles are photons. They'll be radiated in various directions along the neutrinos path. But this is a giant block of naturally formed ice with various impurities in it. They'll be scattered fairly quickly and absorbed not too long after that. Realistically, its very unlikely that you will detect a photon far from where it was generated. So i think what happens is that as a high energy particle streaks through the grid, you get counts from the detectors closest to its path. From that you can probably estimate roughly where it came from.

So I'm curious, energy can neither be created nor destroyed, but apparently it's OK to move it into a place where it rarely interacts with normal matter.

I don't understand this question. Why wouldn't it be ok to take some energy and put it out of the way somewhere? You could do the same thing by pointing a laser pointer into the night sky. Those photons might travel for millions or billions of years before being absorbed by something. Why would thermodynamics care if you wanted to do this?

These particles are photons. They'll be radiated in various directions along the neutrinos path. But this is a giant block of naturally formed ice with various impurities in it. They'll be scattered fairly quickly and absorbed not too long after that. Realistically, its very unlikely that you will detect a photon far from where it was generated. So i think what happens is that as a high energy particle streaks through the grid, you get counts from the detectors closest to its path. From that you can probably estimate roughly where it came from.

It's much better than that. First of all, depending on which part of the array you're talking about, you can detect Cherenkov radiation emitted from mulitple times the distance of the individual detector separations. But that's not the fun part. The fun part is when a neutrino/nucleus interaction results in a muon. The muon will continue in the same direction as the original neutrino. Muons don't decay quickly and don't slow down quickly. They leave nice long tracks through the detector, emitting Cherenkov radiation along the whole length of the track. The detector has an estimated 2 degree resolution for the source direction of muons.

Electrons and taus are the other particles that are created by neutrino interactions. The electrons scatter too quickly to get good directional resolution. Taus decay, so provide interesting cascade events, but aren't really good at providing directional information, either.

EDIT: This page has some example of what the tracks look like. The size of each blob is the amplitude at the detector. I'm not positive, but I believe the color coding just tells you which direction along the track is forwards. Red is the earliest detection and blue is the latest.

EDIT2: I meant to point out that the ice is much more clear than you'd imagine. It does have some dust mixed in, but the pressures have compressed the air bubbles down to de minimis sizes. I couldn't find specific stats, but it's meaningful that I keep seeing it referred to as "ultra-clear".

These particles are photons. They'll be radiated in various directions along the neutrinos path. But this is a giant block of naturally formed ice with various impurities in it. They'll be scattered fairly quickly and absorbed not too long after that. Realistically, its very unlikely that you will detect a photon far from where it was generated. So i think what happens is that as a high energy particle streaks through the grid, you get counts from the detectors closest to its path. From that you can probably estimate roughly where it came from.

It's much better than that. First of all, depending on which part of the array you're talking about, you can detect Cherenkov radiation emitted from mulitple times the distance of the individual detector separations. But that's not the fun part. The fun part is when a neutrino/nucleus interaction results in a muon. The muon will continue in the same direction as the original neutrino. Muons don't decay quickly and don't slow down quickly. They leave nice long tracks through the detector, emitting Cherenkov radiation along the whole length of the track. The detector has an estimated 2 degree resolution for the source direction of muons.

Electrons and taus are the other particles that are created by neutrino interactions. The electrons scatter too quickly to get good directional resolution. Taus decay, so provide interesting cascade events, but aren't really good at providing directional information, either.

Thanks for the description. I didn't realize the decays were so complex.

No. Heavy water was used in some experiments because it increases the chances of a detection. Simple geometry -- deuterium nuclei are twice as big as hydrogen-1 nuclei. The way you detect neutrinos is to wait until one essentially smashes into an atomic nucleus. So if two-thirds of your potential targets are 100% bigger... you've got an advantage.

EDIT: Fixed bad 7th grade math. If something is twice as big, it is 100% bigger, not 50% bigger.

So I'm curious, energy can neither be created nor destroyed, but apparently it's OK to move it into a place where it rarely interacts with normal matter.

I don't understand this question. Why wouldn't it be ok to take some energy and put it out of the way somewhere? You could do the same thing by pointing a laser pointer into the night sky. Those photons might travel for millions or billions of years before being absorbed by something. Why would thermodynamics care if you wanted to do this?

Just a conceptual question about what exactly the definition of "destroyed" is. How inaccessible can energy become before it's considered "destroyed"?

So I'm curious, energy can neither be created nor destroyed, but apparently it's OK to move it into a place where it rarely interacts with normal matter.

I don't understand this question. Why wouldn't it be ok to take some energy and put it out of the way somewhere? You could do the same thing by pointing a laser pointer into the night sky. Those photons might travel for millions or billions of years before being absorbed by something. Why would thermodynamics care if you wanted to do this?

Just a conceptual question about what exactly the definition of "destroyed" is. How inaccessible can energy become before it's considered "destroyed"?

You are getting caught up in a semantic trap that is meaningless. If you try to define the "existence" of energy and where it is exactly created or destroyed, you will get nowhere, because it doesn't even make sense to talk about it being created or destroyed. Energy isn't a "thing", and it is relative, not absolute (e.g. the kinetic energy of any object is entirely dependent on the reference frame chosen).

The rigorous way that energy is thought about in modern terms is through Noether's theorem, which says in a precise mathematical way that conservation of energy is simply another way of saying "the laws of physics are constant over time". That's it. Just put creation and destruction of energy out of your mind forever.

No. Heavy water was used in some experiments because it increases the chances of a detection. Simple geometry -- deuterium nuclei are twice as big as hydrogen-1 nuclei. The way you detect neutrinos is to wait until one essentially smashes into an atomic nucleus. So if two-thirds of your potential targets are 100% bigger... you've got an advantage.

EDIT: Fixed bad 7th grade math. If something is twice as big, it is 100% bigger, not 50% bigger.

If you just wanted to increase detection rates, you'd use liquid scintillator, not heavy water. Sudbury Neutrino Observatory--which is the only one that I am aware of that used heavy water in its detector--used D2O for the very specific reason that they were focused on directly showing that neutrino oscillations occur, and there are reaction channels between neutrons and neutrinos which allow measurement of tau and muon neutrino fluxes directly (albeit not necessarily as efficiently as electron neutrinos). Deuterium was used instead of, say, helium because it's easier to handle (in heavy water) and heavier nuclei have kinematic constrains on some reactions (such as inverse beta decay, although that's an antineutrino thing).

Water, which is mostly protons, wouldn't have allowed them to make the measurements they needed to, and neither would liquid scintillator (also mostly protons).

How much light is generated by cherenkov radiation from a single high energy neutrino? I'm guessing that if these detectors (PMTs?) are frozen into cryogenic ice they probably have insanely low dark counts so maybe not much. Would it be enough to see by eye if you happened to be looking in the right place at the right time? Just a flash of light?

You can see flashes of Cherenkov light from cosmic rays if you close your eyes and pay attention on an airplane. It'll be a pale blue flash. Check out the wikipedia page for Cherenkov light to get an idea about the color. In the case of your eyes charged particles emit light as they travel through the vitreous humor.

Nothing boggles the mind so much as to imagine the lonely journey of trillions upon trillions of neutrinos through my body and the near-empty universe every second. That something so common would bounce off an atom in the south pole a couple times over such a long period... just dizzying. What a weird universe we live in.

I love IceCube. I love imagining the deep boreholes refrozen into a super-clear pitch black abyss with all those electric eyes waiting patiently for the next little blip.

So, a clarification on a point in the article, kinda subtle. You write, "To slow down, they emit detectable Cherenkov radiation." Thing is, the Cherenkov radiation doesn't actually help that much with the slowing down. Ionization and/or bremsstrahlung radiation will be slowing down the particles much more (depending on the type of particle and energy). Cherenkov radiation is really just a tiny fraction of that, but it is useful since it is very reliably directional, and it is emitted at a wavelength for which water or ice is transparent.

On an unrelated note, what's the deal with using the past tense for Super Kamiokande? It still holds over 3 kton of water, and still detects plenty of neutrinos, over 16 years after starting.

Does anyone with a particle physics background know how much energy a neutrino at peta eV levels is carrying? I remember reading an article about the detection of protons accelerated by astrophysical processes so that each proton carries the same kinetic energy as a basketball travelling at 100mph! So how much is this in "real money"?

Does anyone with a particle physics background know how much energy a neutrino at peta eV levels is carrying? I remember reading an article about the detection of protons accelerated by astrophysical processes so that each proton carries the same kinetic energy as a basketball travelling at 100mph! So how much is this in "real money"?

EDIT: Ignore the top part and skip to the Wolfram Alpha quote and then read the post by truth is life

Based on my very rough calculations (eV -> J, J / basketball mass in kg / 1 m * 1 s = m/s) , a neutrino of this energy is equivalent in energy to a basketball traveling 0.001 mph, which is approximately the same speed as the fastest known glacier.

Does anyone with a particle physics background know how much energy a neutrino at peta eV levels is carrying? I remember reading an article about the detection of protons accelerated by astrophysical processes so that each proton carries the same kinetic energy as a basketball travelling at 100mph! So how much is this in "real money"?

Based on my very rough calculations (eV -> J, J / basketball mass in kg / 1 m * 1 s = m/s) , a neutrino of this energy is equivalent in energy to a basketball traveling 0.001 mph, which is approximately the same speed as the fastest known glacier.

I am actually a particle physicist of sorts, and yes, this approach is pretty close to what I would do. I think you lost a factor of two in there, though;

K = 1/2*m*v^2

v = sqrt(2*K/m)

see? This gives me a v (for the basketball) of 0.023 m/s, which is (according to Wolfram Alpha) some 8.4 times faster than a very speedy snail. So, not particularly fast.

The fact that it's a neutrino doesn't enter into it, because the energy is sort of mass independent, in that if the energy is specified it doesn't really matter what the mass is, unless obviously you want to calculate something from the energy that does depend on the mass. If a proton or photon had an energy of 1 PeV, then it would have the same energy. The reason the energy for the Oh-My-God particle (what HydrogenAlpha was probably thinking of) is so much more impressive in layman's terms is that it had an energy of about 100,000 PeV.

Does anyone with a particle physics background know how much energy a neutrino at peta eV levels is carrying? I remember reading an article about the detection of protons accelerated by astrophysical processes so that each proton carries the same kinetic energy as a basketball travelling at 100mph! So how much is this in "real money"?

Based on my very rough calculations (eV -> J, J / basketball mass in kg / 1 m * 1 s = m/s) , a neutrino of this energy is equivalent in energy to a basketball traveling 0.001 mph, which is approximately the same speed as the fastest known glacier.

I am actually a particle physicist of sorts, and yes, this approach is pretty close to what I would do. I think you lost a factor of two in there, though;

K = 1/2*m*v^2

v = sqrt(2*K/m)

see? This gives me a v (for the basketball) of 0.023 m/s, which is (according to Wolfram Alpha) some 8.4 times faster than a very speedy snail. So, not particularly fast.

The fact that it's a neutrino doesn't enter into it, because the energy is sort of mass independent, in that if the energy is specified it doesn't really matter what the mass is, unless obviously you want to calculate something from the energy that does depend on the mass. If a proton or photon had an energy of 1 PeV, then it would have the same energy. The reason the energy for the Oh-My-God particle (what HydrogenAlpha was probably thinking of) is so much more impressive in layman's terms is that it had an energy of about 100,000 PeV.

Haha thanks. I'd like to think I'd have gotten that right if I put more thought into it, but I'll blame it on my lingering flu...

EDIT: And for future reference for inquiring minds, you can actually enter "speed of a basketball with an energy of 1 petaelectronvolt" into Wolfram Alpha and get an answer.

True, but they're subject to redshift, if their origin is sufficiently distant.

Redshift really only applies to photons. However, if the source is far away, a neutrino will appear to have a lower energy in our reference frame. But it really does have the same energy as when it left the source. It's a question of reference frames, not gains/losses of energy.

"take away enough energy that they would move faster than the speed of light in the ice"

The result of the collision with the high energy neutrino is that some of the particles from the ice are accelerated to above the speed of light in ice.

Note that the "speed of light in ice" is less than the "speed of light in a vacuum". It is possible for particles to move faster than the speed of light in a medium (such as ice) and still be going slower than the speed of light in a vacuum. Particles going faster than the speed of light in a medium emit Cherenkov radiation (https://en.wikipedia.org/wiki/Cherenkov_radiation), which can readily be detected.